feat(cli): git repository support for custom init templates

[rohang9000]

Rohan:

Updated code for cdk init command to handle custom templates from Git repository sources. This is compatible with the existing --language and --template-path flags. The --from-git-url flag was added to clone a Git URL that is passed in by the user, clones the repository, extracts the specified template files and initializes new project with them. The cdk init functionality of creating new local Git repo to track changes, making initial commit, and installing project dependencies is maintained.

Added additional tests and implemented changes I had requested. There were 40 commits before, and many merge conflicts from #819.

Unit test coverage for init.ts is now 97.65%. Tested by hand for many cases as well.

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov-commenter]

Codecov Report

❌ Patch coverage is 93.46405% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.88%. Comparing base (e46adaf) to head (657aaf0).

Files with missing lines	Patch %	Lines
packages/aws-cdk/lib/commands/init/init.ts	93.79%	8 Missing ⚠️
packages/aws-cdk/lib/cli/cli.ts	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #820      +/-   ##
==========================================
+ Coverage   82.76%   82.88%   +0.12%     
==========================================
  Files          71       71              
  Lines       10396    10519     +123     
  Branches     1295     1320      +25     
==========================================
+ Hits         8604     8719     +115     
- Misses       1753     1762       +9     
+ Partials       39       38       -1     

Flag	Coverage Δ
suite.unit	82.88% <93.46%> (+0.12%)	⬆️

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[iankhou]

Probably will need to wait until #819 is merged.

[iankhou]

This should be replaced by a check that ensures that from-path or from-git-url was also used.

[iankhou]

why not use a check in yargs instead? In general, try to catch problems as early as you can.